While I was working with the Pokeberries I also harvested some Tansy leaves from the garden.
Most dye resources mention only the flowers. I got a lovely bright at the same time mellow yellow on some Lion Brand Fishermen's Wool. Here it is right out of the dye bath.
I gathered about 175 grams or so of tansy leaves still on the stems then added enough water to cover them. I brought them to a boil then put them on simmer for 30 minutes. Let cool over night and repeated the same in the morning.
I transferred the dye liquor with the leaves in another bin while I mordant the yarn with Alum and CoT assist. I used about 2T Alum and 2t CoT for about 175 grams of Lionbrand Fishermen's Wool.
Then I removed the leaves from the dye liquor. I drained the mordant water off. Then added the dye liquor to the pot with the fiber and cooked it at 180 deg F for 45 min give or take and let cool over night.
Here's the lovely dye all dried and ready for some mittens.
Here a comparison of the Tansy dyed yarn and a small sample of Dandelion flower dyed yarn I did earlier this summer.